Had to reset & restore my phone and want it the way it was before. The old profile is still there on my PC but BS wants to create a new one.
How can I get BS to use the old profile? Is there a file I can edit?

I'm sorry for the late answer. I missed this thread. Some modifications were investigated to easy the setup process, but it was necessary to focus on Thunderbird/Mozilla last evolutions which required the complete rewriting of the add-on.

Had to reset & restore my phone and want it the way it was before. The old profile is still there on my PC but BS wants to create a new one.
How can I get BS to use the old profile? Is there a file I can edit?

When you say "old profile", do you mean the old Android source declared in BirdieSync Configuration ? Usually "profile" is a notion used with Thunderbird.
Did you want that BirdieSync server identifies the restored Android phone as the old one declared in BirdieSync Configuration and not as a new Android source ? (that can happen if BirdieSync data were cleared on the Android device)
If yes, it would be better to contact support(at)birdiesync.com in order to do it since it would require modifications of BirdieSync configuration which cannot be easily done.